flashing. Procedures vary somewhat depending upon the type of roofing material. For residential work, where shingles are the most common type of roofing material, the plumber can install the flashing. Care must be taken to correctly place the flashing between the courses of shingles and to avoid damaging surrounding shingles. The flashing must be installed before the stack is put into position so that it can be fit under the shingles, as shown in Figure 19-12. The first step is to locate where the stack will go through the roof. This can be done by extending a length of pipe through the opening in the double plate at the top of the wall until it touches the underside of the roof sheathing. Check the pipe for plumb and mark the location of the pipe on the sheathing. If roof framing prohibits vertical installation, the vent will need to be offset to avoid cutting framing members. It is generally easier to cut the opening from above the roof using a reciprocating saw. Drive a nail through the sheathing from the underside to transfer the location of the hole to the topside of the roof. Cut the hole approximately 1″–2″ larger in diameter than the vent pipe. Carefully raise the shingles around the hole, using a flat pry bar. Remove enough nails to allow the shingles to be lifted. Place the flashing over the hole and mark the shingles that need to be trimmed. Make the necessary cuts and check the fit. Once the fit is correct, slide the flashing under the shingles into the position shown in Figure 19-12. Renail the shingles beginning with the highest course. Note that no roofing nails should be exposed. The bottom edge of the flashing is not nailed. Extending the stack through the roof requires pipe and at least one coupling because the distance will most likely be more than 10′. Extend the stack through the ceiling and add an increaser and a larger pipe, Figure 19-11. The amount of pipe that must extend above the roof is specified by code. Be aware that walls extending above the roof near where the vent is to be located can effect the height of the vent above the roof. Because tall vents are generally undesirable, it may be neces- sary to offset the vent so it can extend through the roof at a point where it will be less conspicuous. In cold climates, it is desirable to use larger pipe above the insulated area of the building to reduce the possibility of the vent becoming blocked by frozen condensation. One of the most important parts of installing the stack is to make sure the flashing is correctly installed. Flashing is material (often a formed metal or plastic product) that is used to prevent water from leaking into the building around the stack. If the finished roof has not been installed, the roofing contractor can install the flashing during the roofing process. If the roofing material is already in place, the plumber may need to install the Roofing Flashing Rafter Vent increaser Ceiling Vent stack Sanitary tee Goodheart-Willcox Publisher Figure 19-11. An increaser is installed on stack before it extends through roof. Goodheart-Willcox Publisher Figure 19-12. Installing vent flashing involves cutting a hole through the shingles and roof sheathing and then trimming the shingles to fit around the flashing. 306 Section 3 Plumbing System Design and Installation Copyright Goodheart-Willcox Co., Inc.